Improve registry hot paths

[ricardo-devis-agullo]

Three low-risk refactors on registry request‑hot paths that reduce per‑request allocations and avoid unnecessary I/O:

1. get-component: Replace split/map/split with single‑pass template header parsing
   The per‑render parseTemplatesHeader now walks the header string once instead of twice.
   Result: ~3.4× faster on a 20‑template header.

2. get-component: Use Set.has + for‑in loop for custom‑header filtering
   The per‑render filterCustomHeaders builds a skip‑set once and iterates with for‑in instead of Object.entries().filter().fromEntries() with repeated includes().
   Result: ~4.9× faster on an 80‑header map with 20 skip entries.

3. components-details: Replace deep structuredClone/JSON.parse(JSON.stringify()) with shallow per‑component copies
   getFromDirectories no longer clones the entire details object before scanning for missing components.
   Result: ~4× faster on a 1000‑component / 5-version datastore.

4. repository: Memoize local component discovery when hotReloading is off
   The local.getComponents() filesystem scan is cached after the first call to avoid repeated readdirSync + lstatSync calls.

All existing 838 tests pass without modification. No breaking changes.